Black hole decay

When I read the security report from Cern (not that I am too worried), I came to something, which I do not fully understand:
As we all know, we are save from micro black holes created at the LHC because of Hawking radiation (for one of many reasons). The Cern people push this argument further and say, even if Hawking radiation does not exist, micro black holes will decay by their inverse creation process with a decay time of order 1/mass on general grounds of qm, since no symmetry forbids this. (CPT theorem)
Ok, fine, but what about macroscopic black holes, Their decay time should then be rather enormous. I know, I know, we have to worry very much about entropy here, but how exactly do these entropy arguments enter quantum field theory? Microscopic black holes are often said to be similar to elementary particles. It seems there is some limit here to do so.